1. Field of the Invention
The present invention relates to a wireless local area network (WLAN) device that can receive and transmit signals of multiple modulation types. In particular, the present invention relates to a sequencing interpolator that can provide a rational ratio (integer/integer) interpolation for signals of a predetermined modulation type, thereby reducing the number of phase locked loops (PLLs) to be used in the WLAN device.
2. Description of the Related Art
Wireless local area networks (WLANs) are becoming increasingly popular as communication networks. The IEEE 802.11 standards provide guidelines for the operation of devices operating in WLANs. Specifically, the 802.11a standard defines communication in the 5 GHz band using data rates of 6, 12, 18, 24, 36, and 54 Mbps. The 802.11b standard defines communication in the 2.4 GHz band using data rates of 1, 2, 5.5, and 11 Mbps. A recent proposed addition to the 802.11 standards, called the 802.11g standard, uses the high data rates of 802.11a in the frequency band of 802.11b, i.e. 2.4 GHz.
The 802.11g standard envisions that 802.11b devices can communicate with 802.11g devices that operate in the same WLAN, irrespective of communication mode. In an infrastructure communication mode, clients communicate with each other through an access point. In other words, an access point functions as a communication hub between its associated clients. In contrast, in an ad hoc communication mode, clients can communicate with each other directly. As used herein, the term “device” can refer to either an access point or a client.
To ensure backwards compatibility with 802.11b devices while allowing data rate increases, the 802.11g standard incorporates the modulation schemes from both the 802.11a and 802.11b standards. In general, modulation refers to the addition of information to a carrier. Typical modulation techniques include frequency modulation wherein the frequency of the carrier waveform is varied. The 802.11b standard uses a modulation scheme called complementary code keying (CCK) whereas the 802.11a standard uses another modulation scheme called orthogonal frequency division multiplexing (OFDM). Both CCK and OFDM provide distinctive frequency modulation aspects.
The 802.11g standard, although providing guidelines for compatibility, allows the dual modulation schemes to be implemented in a proprietary manner. Thus, some WLAN device providers could use redundant components to ensure that signals received or transmitted using CCK or OFDM modulation can be correctly interpreted and reconstructed. However, this redundancy undesirably increases the cost and power consumption of the network. Therefore, a need arises for a method of efficiently reducing component redundancy and power in a WLAN device (access point and/or client) operating in accordance with the 802.11g standard.